The novels are not the movies. They are EU. There is no Force Shield, at least not from what it looks like in the movies. Fact is typically your opponent is in your face with his lightsaber and there is no time to focus on using the force for attack, lest you get chopped up. A superior duelist and force user however, can still find a way to use the force for attacking, like Maul did on Obi Wan, Dooku did on Obi Wan in ROTS (Choke), etc etc. However, it is quite clear that Jedi and Sith use the Force to anticipate their opponents actions and react to it. This is what Obi Wan was training Luke in on the Falcon when he made Luke cover his eyes and try and deflect bolts. This is how Jedi can deflect blaster bolts as they come too fast to deflect via sight alone. And yes, Jedi use the force to jump and flip around in duels to gain tactical advantage. That said, the Force Sheild idea is not bad by any means. It would make sense to have some sort of an invisible mystical barrier of the Force that prevents telekinetic Force attacks. But if that were true, and if Obi Wan did let down his barrier to be allowed to be pushed/coked/etc why wouldn't the Sith just chop him with his lightsaber, because lowering the barrier would mean Obi Wan wasn't using the Force, which means he would be unable to forsee the next strike(s) of the Sith.